U.S. iPhone and iPad sales skewed more toward devices with less storage space in the March quarter compared to the final three-month period of 2013.

U.S. iPhone and iPad sales skewed more toward devices with less storage space in the March quarter compared to the final three-month period of 2013, a research firm said today.

According to a poll conducted by Consumer Intelligence Research Partners (CIRP), U.S. Apple customers downsized the storage sizes of their iPhone and iPad between 4% and 12% in the just-completed quarter.

The largest decrease in average storage capacity was for Apple's flagship iPhone 5S, which fell from 29.1GB in the December quarter to 25.7GB in the March quarter. The latter was down 11.7% from the former.

Averages for the iPhone 5C and the iPad Air slid 8.6% in the March period, while storage for the Retina-equipped iPad Mini slipped 3.7%.

Apple charges a $100 premium for each step in storage space for both the iPhone and iPad, and most of that is pure profit. An iPad Air with 16GB retails for $499, while the same tablet with 32GB runs $599, but Apple pays only $9 more for the memory in the latter, according to tear-down experts at IHS iSuppli.

At the same time, CIRP's survey of 500 Americans who bought an iPhone, iPad or Mac in the January-March stretch showed that buyers leaned more toward the top-end models than in the same quarter the year prior.

In the all-iPhone bucket, 62% of those sold were the iPhone 5S, compared to 53% of the then-top-tier iPhone 5 in early 2013. The iPad Air accounted for 47% of all iPads bought by the polled consumers in the first three months of this year, 12 percentage points more than the then-flagship Retina iPad during the first quarter of 2013.

"Apple sold relatively cheaper storage configurations for these leading products. After the holiday quarter, buyers seemed to gravitate to the flagship models, while economizing with smaller storage capacity," said Mike Levin, co-founder and analyst at CIRP, in a statement. "We expect to see stable or even slightly lower U.S. ASPs as a result."